The present invention relates to a variable geometry exhaust nozzle for a turbojet engine, more particularly such a nozzle in which the nozzle opening in the converging-diverging configuration may be controlled by a single control system.
Variable geometry exhaust nozzles are well-known in the art and typically comprise an annulus of upstream flaps pivotally connected to the exhaust duct of the turbojet engine and an annulus of downstream flaps which are pivotally attached to downstream edges of the upstream flaps. As is known in the art, a control system may be connected to selected ones of the flaps to vary the opening of the exhaust nozzle, as well as its configuration.
Jet aircraft must often carry out missions using both subsonic and supersonic flight. In such cases, the turbojet engines may be equipped with an afterburner system and the variable cross-section nozzle may be moved from a converging-converging configuration for subsonic flight to a converging-diverging configuration for supersonic flight. Moreover, it is often necessary to adjust the minimum nozzle cross-sectional area as a function of the operational state of the engine, particularly a lesser cross-sectional area in normal operation and an enlarged cross-sectional area when using the afterburner.
French patent 1,225,736 illustrate a type of this known nozzle. In this structure, the upstream and downstream flaps use separate controls, each comprising hydraulic actuating cylinders which are connected to the flaps by means of link rods or hinging systems with an annulus of outer flaps being connected to the downstream flaps by link rods. These systems use two separate control loops. While this system achieves independent control of each set of flaps, it results in a structure which is rather complex and fairly heavy.
In the nozzle structure illustrated in French Patent 2,602,274, the downstream flaps are controlled by cylinder rods which are connected by link rods to the outer flaps which, in turn, are connected by link rods to the downstream flaps. In this structure, the relative positions of the three sets of flaps are defined by the lengths of the actuating cylinder rods. Moreover, each control flap of a particular set is connected by two link rods to the outer ring to assure synchronization of operation and to provide a back-up system in the event of failure of one or more of the actuating cylinders. Again, this structure is rather complex and fairly heavy.